I don't find horticulture-grade pumice available locally. So, I bought some scoria and sifted it. I got three grain sizes, with two shown here:
The third is whatever passed through the finest sieve. It is the finest, still coarser than regular sand but full of dust. I have kept it until I find what to do with it.
My question - Which to use for the following plants: Haworthia, Gasteria, Aloe, Echeveria and its allied species. Is the finer grain of any use?
My climate - Csa according to the köppen climate classification: hot Mediterranean.
Edit: Climatic data for Tel-Aviv in this link. No rainfall in summer (but very humid), high rainfall in winter.
Do I need to add water-retaining mediums, such as peat or vermiculite? I grow my collection items in unglazed pots. Rooted cuttings from trimming are grown in plastic pots.